Normal thyroid function in pregnant women is essential to brain development in their children. Recent data suggests that even in asymptomatic women with subclinical hypothyroidism, intelligence of their offspring is affected. The Maternal-Fetal Medicine Units (MFMU) Network of the NICHD is currently prospectively evaluating in a multicenter randomized trial whether thyroid hormone replacement for women with subclinical disease improves outcomes for their children. An expert panel from the U.S. National Research Council reports that 3 percent of developmental disabilities are a direct result of exposure to environmental exposures, and a greater percentage arise from interactions between environmental agents and individual genetic susceptibility. There is widespread human exposure to the industrial chemicals PBDE and perchlorate, endocrine disruptors which have been shown to interfere with thyroid function in animals. We plan to investigate whether these agents also interfere with thyroid function in pregnant women and assess potential effects on neurological development of prenatally exposed children. In collaboration with the environmental health scientists at Columbia University, we intend to recruit pregnant women from the MFMU trial into an ancillary study to assess levels of PBDE and perchlorate and determine whether these endocrine disruptors have a measurable affect on maternal thyroid function tests. Children from these pregnancies would be assessed initially at one year of age to evaluate potential differences in outcomes as assessed by the Bayley's Developmental Quotient. If a relationship between PBDE or perchlorate exposure and thyroid function were evident, we would seek additional funding to study potential differences in childhood development until age five. PUBLIC HEALTH RELEVANCE: Normal thyroid function in pregnant women is essential to fetal brain development. There is widespread human exposure to the industrial chemicals PBDE and perchlorate, endocrine disruptors which have been shown to interfere with thyroid function in animals. We plan to investigate whether these agents interfere with thyroid function in pregnant women and assess whether they have adverse effects on neurodevelopment in prenatally exposed children.